When casting some metals, the reactivity of the metal produces oxide films and other inclusions that pose difficulties that are not encountered when casting less reactive metals. For example, the very reactive nature of oxygen with metallic aluminum, especially in the molten state, can result in oxide films that can be formed during the pour and then folded back onto themselves in the cast product. These so-called bifilms can lie behind most, if not all, of the casting problems associated with aluminum, including porosity, hot tears, low mechanical properties and corrosion initiation.
These concerns are not limited to aluminum. While casting certain steels, elements in the steel can also oxidize during the process, forming ceroxide inclusions that can result in low tensile strengths, low yield strengths, etc.
It is generally known to pour molten metal downwardly into the mold, using gravity. In such cases, known technology is used for the filling cup or sleeve used to introduce the molten metal. It may be desirable in some situations to provide a system in which a charge of the molten metal is pushed upwardly, that is, against the flow of gravity, into the mold. In these cases, the bi-directional flow provided by the known filling sleeve technology presents a problem, as the metal will drain out of the mold once the pushing force is removed.
In WO 01/26843, a check valve is disclosed for use with upwardly flowing molten metal in a casting operation, but that invention uses a spherical valve member that moves within a valve compartment. At the lower end of the valve compartment, the spherical valve member seats itself in a circular aperture that seals against downward flow. At the upper end of the valve compartment, the spherical valve member is stopped against a non-circular (typically, oval) aperture, but the incomplete fit allows upward flow in the open area between the spherical valve member and the non-circular aperture. Little or no filtering of the molten metal is provided by this method.
It is therefore an unmet advantage of the prior art to provide a filing cup or sleeve for use in pouring molten metal into a mold against the flow of gravity having a filtering check valve.